At present, different alert and maritime safety systems are known for the rescue of crew members who have fallen into the water, also known as PLB (Personal Locator Beacon) systems for situations of “man overboard” (MOB).
Said systems are generally based on emitter devices that work in the international rescue frequency, 121.5 MHz for civil use, and 243 MHz for military, and that due to the short range of its emission are only received by ships with receivers in said frequencies, which sail close to the accident (maximum 4-5 nautical miles).
Within these systems there are various modes of operation, with a greater or lesser success, which transmit the position of the shipwrecked person by the incorporation of a Global Positioning System (GPS, GLONASS, GALILEO, . . . ), hereinafter GPS, and the encoding of said position in the carrier wave, with the drawback of requiring a decoder onboard, specific for each manufacturer as there does not exist a coding regulation of said signal.
Likewise, global positioning systems are known, both of personal use and for the own ship, which, based on the different satellite navigation systems recognized by the GMDSS system (such as COSPAS SARSAT, GALILEO, GLONASS), send the satellites data regarding the position and identification of the victim using the 406 MHz frequency, and this information later reaches the maritime rescue coordination centres onshore, which report to the national authorities in whose waters the accident has occurred. These systems are not recognized for personal use nor are they accepted by the International Maritime Organization (IMO) or the International Convention for the Safety of Life at Sea (SOLAS).
On the other hand, signal emitting equipment of the MOB emergency signal by the name “Digital Selective Calling” (DSC) are currently on the market. DSC emissions are a subsystem of the GMDSS global system, which regulates all onboard safety and radio communication means. Said DSC call is a call which exclusively transmits data in communication channel 70, and it has several levels of severity (distress, urgent and safety). Again, both IMO and SOLAS are against the indiscriminate use of said channel 70 for personal use by the shipwrecked person, though not of the ship, faced with the possibility of generating a huge number of calls produced by false alarms, improper use, etc., causing a saturation of the channel. It is for this reason that it is desirable to look for a way to limit the use of said channel 70.
Finally, PLB-AIS calls are known, which using the AIS (Automatic Identification System) system, emit every given period of time, in accordance with the vessel speed but with a minimum of at least one emission every 5 minutes. Generally, the identifying data of the transmitter are the MMSI, position, speed and course. This emission is performed via VHF (emission in the frequencies of 161975 MHz and 162025 MHz), but unlike previous systems they do not give an alarm system, but simply inform of a position, which in principle shall be confused with that of a ship and not that of a shipwrecked person in MOB situation.
More specifically, emitter-receiver systems are known wherein the person who has fallen into the water emits a radiofrequency signal that is initially received by the vessels nearby the accident, and which is sent to shore by repetition of stations in vessels, called “MAYDAY RELAY”, until reaching a coastguards station located onshore, which coordinates the alarm and rescue process.
The technical problem posed here is that the current location systems do not allow a repeated search in terms of the location of the vessels in the immediate vicinity of the own ship (ship from which a crew member has fallen), so that with said current systems, if the own ship does not respond after the call of the shipwrecked person, there is no possible identification thereof by another vessels which may be a few miles away, the last hope remaining, and only if a general DSC call of maximum priority has been made, called “MAYDAY”, that the coastguards station has correctly received the coordinates of the shipwrecked person, this way of acting being very slow, dangerous and can clearly be optimized, as in these cases of extreme urgency every minute that passes is of vital importance. The ships located in the VHF range of the general DSC call will also receive the alarm signal, but will wait for the coastguard's station to check the veracity of said alarm, to then be coordinated by it to collaborate in the rescue, if possible. But as mentioned above, this type of general DSC call is totally questioned by the IMO, and it will be very difficult for it to be implemented in the GMDSS system of global application with no type of modification.